1. Field of the Invention
The present invention relates to a medium voltage switchgear having a circuit breaker, the circuit breaker having a charging motor actuated by a control switch with a switch lever, the switch lever engaging a control cam having a relief channel.
2. Background Information
A medium voltage switchgear typically comprises a switching mechanism housed in an enclosure. The switching mechanism, typically a circuit breaker, includes separable contacts for each phase and a common spring operated closing and tripping device. This device includes one or more opening springs which separates the contacts and a pair of closing springs which close the contacts and charge the opening spring. The separable contacts are closed by releasing the energy stored in the closing springs through activation of a closing trigger mechanism. This can be done manually or remotely through a solenoid. An electronic trip circuit monitors the load currents and actuates an opening trigger mechanism through an opening solenoid if the current exceeds certain current-time characteristics. The closing springs are charged manually by a lever arm through a ratchet coupling, or, more preferably, by a motor.
The motor is coupled to a crank shaft. The crank shaft is further coupled to the closing springs, the opening springs and a pole shaft. The pole shaft is coupled to the contacts. In operation, the motor rotates the crank shaft to charge the closing springs. When the closing springs are released, the closing springs cause the crank shaft to rotate and this motion is transferred to the pole shaft which closes the contacts. At this point, the closing springs are typically recharged so that the circuit breaker may be closed again after being tripped.
The motor may be controlled by a motor control switch mounted adjacent to the crank shaft. The motor control switch includes a switch lever that contacts a motor control cam. The motor control cam is fixedly coupled to the crank shaft and has a cam surface with a first, reduced diameter portion and a second, wide diameter portion. Each portion of the cam surface extends about 180 degrees about the motor control cam. At one boundary between the first, reduced diameter portion and the second, wide diameter portion is a switch lever notch. The switch lever notch is, essentially, a radial edge on the cam surface. When the switch lever is in contact with the first, reduced diameter portion, the motor control switch does not actuate, that is, turn on, the motor. When the switch lever is in contact with the second, wide diameter portion, the motor control switch actuates the motor. The motor control cam is coupled to the crank shaft so that when the closing springs are charged, the switch lever is disposed in the switch lever notch and at the beginning of the first, reduced diameter portion. Thus, when the closing springs are charged, the motor is not actuated. When the closing springs are released, the crank shaft rotates about 180 degrees so that the switch lever is disposed on the second, wide diameter portion. Accordingly, after the closing springs are released, the motor is actuated causing the crank shaft to rotate and charge the closing springs. When the closing springs are charged, the crank shaft has rotated about 180 degrees and the switch lever falls into the switch lever notch, causing the motor to stop. During these operations, the crank shaft, and therefore the motor control cam, are intended to rotate in a single direction.
The disadvantage to this configuration is that various tolerances in the circuit breaker components, wear and tear, and other factors may allow the crank shaft to counter-rotate. That is, the crank shaft, and therefore the motor control cam, may rotate in the opposite direction. Thus, because the switch lever notch is, essentially, a radial edge on the cam surface, counter rotation of the motor control cam may cause the radial edge of the switch lever notch to impact the switch lever. This impact may damage the switch lever or move the switch lever out of the optimal position.
There is, therefore, a need for a motor control cam structured to not impact the switch lever during a counter rotation of the crank shaft.
There is a further need for a motor control cam that may be incorporated into existing circuit breakers.